Comparing the effects of stage and duration of retinoic acid exposure on amphibian limb development: Chronic exposure results in mortality, not limb malformations
Comparing the effects of stage and duration of retinoic acid exposure on amphibian limb development: Chronic exposure results in mortality, not limb malformations
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DOI：
10.1093/toxsci/kfg098
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发表时间：
2003-07-01
影响因子：
3.8
通讯作者：
Ankley, GT
中科院分区：
文献类型：
--
作者：
Degitz, SJ;Holcombe, GW;Ankley, GT
最近，美国各地的两栖动物出现高发畸形的报道。有人认为，这些畸形可能是胚胎发生和蝌蚪发育过程中类维生素A信号通路受到异种物质破坏的结果。因此，进行了一系列实验来检查连续暴露于类视黄醇对非洲爪蟾生命阶段的具体影响。使用柱饱和器和流通稀释器系统提供连续的全反式视黄酸（RA）浓度。第 8 阶段胚胎暴露于 RA 浓度范围为 0.013 至 2 微克/升。在后肢芽出现时（NF阶段48），一部分蝌蚪被转移到干净的水中，其余的生物体通过变态不断暴露。此外，将早期肢芽期蝌蚪暴露于0.031-3μg/l范围内的八个浓度的RA中1周、2周或直到尾部吸收完成。当浓度为 0.24 微克/升及以上时，RA 暴露会导致胚胎死亡率和畸形发生呈浓度依赖性增加。然而，这种早期胚胎暴露并没有导致在干净水中成熟的存活蝌蚪出现后肢异常。在幼虫阶段暴露的任何存活蝌蚪中，RA 不会引起肢体畸形。我们确信所使用的浓度足够高，因为所使用的最高浓度会在开始接触后 2 周内导致 100% 的死亡率。这一结果表明，生长和发育的其他方面（表面上不明显）比骨骼发育对类维生素A更敏感。从这些实验和我们之前的工作中，我们得出结论，类视黄醇模拟物不太可能产生最近在从野外收集的两栖动物中观察到的一系列肢体畸形。
Recently, high frequencies of malformations have been reported in amphibians across the United States. It has been suggested that the malformations may be the result of xenobiotic disruption of retinoid signaling pathways during embryogenesis and tadpole development. Therefore, a series of experiments were undertaken to examine life-stage specific effects of continuous retinoid exposure on Xenopus laevis. Continuous all-trans retinoic acid (RA) concentrations were delivered using a column saturator and a flow-through diluter system. Stage 8 embryos were exposed to RA concentrations ranging from 0.013 to 2 mug/l. At the onset of hindlimb bud emergence (NF stage 48), a subset of tadpoles was moved to clean water, and remaining organisms were exposed continuously through metamorphosis. In addition, early limb-bud-stage tadpoles were exposed for 1 week, 2 weeks, or until tail resorption was complete, to eight concentrations of RA in the range of 0.031-3 mug/l. RA exposure resulted in a concentration-dependent increase in mortality and dysmorphogenesis in embryos at concentrations of 0.24 mug/l and above. However, this early embryonic exposure did not result in hindlimb abnormalities in surviving tadpoles allowed to mature in clean water. RA did not induce limb malformations in any surviving tadpole exposed during larval stages. We are confident that the concentrations used were high enough, given that the highest concentration used resulted in 100% mortality within 2 weeks of initiating the exposure. This result suggests that other aspects of growth and development, which are not externally obvious, are more sensitive to retinoids than skeletal development. From these experiments and our previous work, we conclude that it is unlikely that retinoid mimics would produce the spectrum of limb malformations which recently have been observed in amphibians collected from the field.